U.S. patent application number 13/195334 was filed with the patent office on 2012-02-16 for exposure condition processing method of x-ray ct apparatus and x-ray ct apparatus.
This patent application is currently assigned to TOSHIBA MEDICAL SYSTEMS CORPORATION. Invention is credited to Gen KONDO.
Application Number | 20120039432 13/195334 |
Document ID | / |
Family ID | 45564829 |
Filed Date | 2012-02-16 |
United States Patent
Application |
20120039432 |
Kind Code |
A1 |
KONDO; Gen |
February 16, 2012 |
EXPOSURE CONDITION PROCESSING METHOD OF X-RAY CT APPARATUS AND
X-RAY CT APPARATUS
Abstract
An exposure condition processing method for an X-ray CT
apparatus according to the embodiment includes: a step in which a
first X-ray emitting condition and a second X-ray emitting
condition for the X-ray CT apparatus are input to a processor; a
step in which the processor, based on the first X-ray emitting
condition and the second X-ray emitting condition, acquires
interval times for switching the first X-ray scanning with the
first X-ray emitting condition, and the second X-ray scanning with
the second X-ray emitting condition; a step in which the processor,
based on the rotation speed of a gantry in the X-ray CT apparatus
that is previously stored in a memory and the interval times,
calculates the frequency of intermittent emission of an X-ray, with
respect to the rotation speed of the gantry.
Inventors: |
KONDO; Gen; (Otawara-shi,
JP) |
Assignee: |
TOSHIBA MEDICAL SYSTEMS
CORPORATION
Otawara-shi
JP
KABUSHIKI KAISHA TOSHIBA
Tokyo
JP
|
Family ID: |
45564829 |
Appl. No.: |
13/195334 |
Filed: |
August 1, 2011 |
Current U.S.
Class: |
378/4 |
Current CPC
Class: |
A61B 6/482 20130101;
A61B 6/545 20130101; A61B 6/405 20130101 |
Class at
Publication: |
378/4 |
International
Class: |
A61B 6/03 20060101
A61B006/03 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 10, 2010 |
JP |
2010-179178 |
Claims
1. An exposure condition processing method for an X-ray CT
apparatus, comprising: a step in which a first X-ray emitting
condition for the X-ray CT apparatus and a second X-ray emitting
condition, which is different from said first X-ray emitting
condition, are input to a processor; a step in which said
processor, based on said first X-ray emitting condition and said
second X-ray emitting condition, acquires interval times for
switching the first X-ray scanning with said first X-ray emitting
condition, and the second X-ray scanning with said second X-ray
emitting condition; and a step in which said processor, based on
the rotation speed of a gantry in said X-ray CT apparatus that is
previously stored in a memory and said interval times, calculates
the frequency of intermittent emission of an X-ray, with respect to
said rotation speed of the gantry.
2. An exposure condition processing method for an X-ray CT
apparatus, comprising: a step in which the rotation speed of a
gantry in an X-ray CT apparatus is input to a processor; a step in
which the frequency of intermittent emission that is set with
respect to said rotation speed of the gantry is input to said
processor; a step in which said processor, based on said set
rotation speed of the gantry and said frequency of intermittent
emission, calculates interval times for switching the first X-ray
scanning with a first X-ray emitting condition, and the second
X-ray scanning with a second X-ray emitting condition, which is
different from said first X-ray emitting condition; and a step in
which said processor, based on said interval times, acquires said
first X-ray emitting condition and said second X-ray emitting
condition.
3. The exposure condition processing method for the X-ray CT
apparatus, according to claim 1 or claim 2, further comprising: a
step in which a display of said X-ray CT apparatus displays at
least one of said rotation speed of the gantry, said frequency of
intermittent emission, said first X-ray emitting condition, and
said second X-ray emitting condition.
4. The exposure condition processing method for the X-ray CT
apparatus, according to claim 1, further comprising: a step in
which said processor, based on said rotation speed of the gantry,
said frequency of intermittent emission, and the number of X-ray
emissions during X-ray scanning with said X-ray CT apparatus that
is previously set, calculates the total exposure time to perform
said first X-ray scanning and said second X-ray scanning.
5. The exposure condition processing method for the X-ray CT
apparatus, according to claim 4, comprising: a step in which said
display displays said total exposure time.
6. The exposure condition processing method for an X-ray CT
apparatus, according to claim 5, further comprising: a priority
condition input step for inputting, with respect to said processor,
for an X-ray image obtained from said X-ray scanning, whether to
select a condition of prioritizing the contrast or a condition of
prioritizing time resolution; wherein, displayed on said display,
is at least one of said rotation speed of the gantry, said
frequency of intermittent emission, said first X-ray emitting
condition, said second X-ray emitting condition, and said total
exposure time, corresponding to the condition input by said
priority condition input step.
7. An X-ray CT apparatus, comprising: a bed on which a subject is
disposed; a gantry configured to include an X-ray emitting part
that emits an X-ray and an X-ray detector that detects said X-ray
that penetrates through said subject; an input part; a determining
part that, based on the input by said input part, determines a
first X-ray emitting condition for said X-ray emitting part, and a
second X-ray emitting condition, which is different from said first
X-ray emitting condition; an acquiring part that, based on said
first X-ray emitting condition and said second X-ray emitting
condition, which are determined by said condition determining part,
acquires interval times for switching the first X-ray scanning with
said first X-ray emitting condition, and the second X-ray scanning
with said second X-ray emitting condition; and a first calculating
part that, based on the rotation speed of said gantry that is
stored previously in a memory and said interval times, calculates
the frequency of intermittent emission of the X-ray, with respect
to said rotation speed of the gantry.
8. An X-ray CT apparatus, comprising: a bed on which a subject is
disposed; a gantry configured to include an X-ray emitting part
that emits an X-ray and an X-ray detector that detects said X-ray
that penetrates through said subject; an input part; a determining
part that, based on the input by said input part, determines the
rotation speed of said gantry and the frequency of intermittent
emission; a first calculating part that, based on said rotation
speed of the gantry and said frequency of intermittent emission,
calculates interval times for switching the first X-ray scanning
with a first X-ray emitting condition, and the second X-ray
scanning with a second X-ray emitting condition, which is different
from said first X-ray emitting condition; and an acquiring part
that, based on said interval times, acquires said first X-ray
emitting condition and said second X-ray emitting condition.
9. The X-ray CT apparatus according to claim 7 or claim 8,
comprising: a display that can display at least one of said
rotation speed of the gantry, said frequency of intermittent
emission, said first X-ray emitting condition, and said second
X-ray emitting condition.
10. The X-ray CT apparatus according to claim 7, comprising: a
second calculating part that, based on said rotation speed of the
gantry, said frequency of intermittent emission, and the number of
X-ray emissions during X-ray scanning with said X-ray CT apparatus
that is previously set, calculates the total exposure time to
perform said first X-ray scanning and said second X-ray
scanning.
11. The X-ray CT apparatus according to claim 10, wherein said
display displays said total exposure time.
12. The X-ray CT apparatus according to claim 11, further
comprising: a priority condition selecting part that, based on the
input by said input part, for an X-ray image obtained from said
X-ray scanning, selects a condition of prioritizing the contrast or
a condition of prioritizing time resolution, wherein, displayed on
said display, is at least one of said rotation speed of the gantry,
said frequency of intermittent emission, said first X-ray emitting
condition, said second X-ray emitting condition, and said total
exposure time, corresponding to the condition selected by said
priority condition selecting part.
13. The X-ray CT apparatus according to either one of claim 8,
comprising: a second calculating part that, based on said rotation
speed of the gantry, said frequency of intermittent emission, and
the number of X-ray emissions during X-ray scanning with said X-ray
CT apparatus that is previously set, calculates the total exposure
time to perform said first X-ray scanning and said second X-ray
scanning.
14. The X-ray CT apparatus according to claim 13, wherein said
display displays said total exposure time.
15. The X-ray CT apparatus according to claim 14, further
comprising: a priority condition selecting part that, based on the
input by said input part, for an X-ray image obtained from said
X-ray scanning, selects a condition of prioritizing the contract or
a condition of prioritizing time resolution, wherein, displayed on
said display, is at least one of said rotation speed of the gantry,
said frequency of intermittent emission, said first X-ray emitting
condition, said second X-ray emitting condition, and said total
exposure time, corresponding to the condition selected by said
priority condition selecting part.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is based upon and claims the benefit of
priority from Japanese Patent Application No. 2010-179178, filed
Aug. 10, 2010; the entire contents of which are incorporated herein
by reference.
FIELD
[0002] Embodiments of the present invention relate to an exposure
condition processing method of an X-ray CT apparatus; and an X-ray
CT apparatus.
BACKGROUND
[0003] An X-ray CT apparatus is a diagnostic imaging apparatus that
emits X-rays, detects the X-rays which have penetrated through a
subject, and reconstructs the image of the subject from the
projection data showing the intensity of the detected X-rays.
[0004] As a scanning method using the X-ray CT apparatus, for
example, dynamic volume scanning and helical scanning are well
known.
[0005] Volume scanning refers to a method in which a plurality of
detectors (for example, several hundred rows) are provided, and by
rotating these detectors around a fixed subject, for an organ
approximately the size of a heart, 3-dimensional data thereof can
be acquired with one scan. Moreover, dynamic scanning refers to a
method in which movement of the subject is photographed by
performing X-ray scanning on the subject into which a contrast
agent is injected. Dynamic volume scanning refers to the
combination of these methods.
[0006] Moreover, helical scanning refers to a method in which while
scanning is performed with detectors that are continuously rotated
at a high speed, by simultaneously moving the bed on which the
subject is placed at a constant speed, a plurality of
cross-sectional scans are completed in a short period of time.
[0007] Moreover, a well-known method referred to as the dual energy
method can be used in combination with these scanning methods.
[0008] This method sequentially performs, with respect to the same
site of the subject, X-ray scanning with a high tube voltage and
X-ray scanning with a low tube voltage, generating a difference
image based on the two X-ray image data obtained using X-rays of
different radiation quality.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is an outline view of an X-ray CT apparatus according
to the first and second embodiments.
[0010] FIG. 2 is a block diagram of the X-ray CT apparatus
according to the first and second embodiments.
[0011] FIG. 3 is an explanation drawing regarding a dual energy
method according to the first and second embodiments.
[0012] FIG. 4 is a block diagram of a processor according to the
first embodiment.
[0013] FIG. 5 is a flowchart of the X-ray CT apparatus according to
the first embodiment.
[0014] FIG. 6 is a block diagram of a processor according to the
second embodiment.
[0015] FIG. 7 is a flowchart of the X-ray CT apparatus according to
the second embodiment.
DETAILED DESCRIPTION
[0016] An exposure condition processing method of an X-ray CT
apparatus according to the embodiment has a step in which a first
X-ray emitting condition for the X-ray CT apparatus and a second
X-ray emitting condition, which is different from the first X-ray
emitting condition, are input to a processor. Furthermore, it
involves a step in which the processor, based on the first X-ray
emitting condition and the second X-ray emitting condition,
acquires interval times for switching the first X-ray scanning,
resulting from the first X-ray emitting condition, and the second
X-ray scanning, resulting from the second X-ray emitting condition.
Furthermore, it involves a step in which the processor, based on
the rotation speed of a gantry in the X-ray CT apparatus and the
interval times, which are previously stored in a memory, calculates
the frequency of intermittent emission of an X-ray, with respect to
the rotation speed of the gantry.
(Device Configuration)
[0017] First, using FIG. 1 and FIG. 2, the configuration of an
X-ray CT apparatus 1 that is common for a first embodiment and a
second embodiment is explained.
[0018] The X-ray CT apparatus 1 is a diagnostic imaging apparatus
that detects X-rays which have penetrated through a subject by
emitting X-rays, and reconstructs the image of the subject from the
projection data showing the intensity of the detected X-rays. This
X-ray CT apparatus 1 is provided with a gantry 3, a bed 4, and a
console 5.
[0019] The gantry 3 performs irradiation of X-rays and detection of
the X-rays that has penetrated a subject 2. Housed inside the
gantry 3 are an X-ray emitting part 3a having an X-ray tube that
irradiates X-rays as a high voltage is applied from a high-voltage
generator, not shown in the figures, and an X-ray detector 3b that
detects the X-rays penetrating the subject 2. Note that the X-ray
emitting part 3a and the X-ray detector 3b are disposed on a
rotation base, not shown in the figures. The rotation base is
disposed inside the gantry 3 so as to rotate around the subject 2.
In the present embodiment, this "rotation of the rotation base" may
be referred to as being the same as "rotation of the gantry 3." For
example, "the rotation speed of the gantry" refers to the rotation
speed of the rotation base.
[0020] The bed 4 has a table-top 4a. The subject 2 is disposed on
the table-top 4a. The table-top 4a, based on a command from a
controller 5b, which is described subsequently, is constituted so
as to be movable with respect to the bed 4, while disposing the
subject 2.
[0021] An input part 5a for external input is disposed on the
console 5.
[0022] Moreover, the controller 5b that controls the actions for
the entire X-ray CT apparatus is disposed on the console 5.
Further, disposed on the console 5 is a processor 5c that processes
an X-ray exposure condition, based on an input command from the
input part 5a, and performs reconstruction processing of X-ray
detection results from the X-ray detector 3b for an X-ray image.
Processing of the X-ray exposure condition by the processor 5c is
described subsequently.
[0023] Moreover, disposed on the console 5 is a scan condition
determining part 5d that determines a scan condition (described
subsequently), based on the input command from the input part
5a.
[0024] Moreover, disposed on the console 5 is a priority condition
selecting part 5e that selects a priority condition (described
subsequently) stored in a memory 5f, which is described
subsequently, based on the input command from the input part 5a.
Moreover, disposed on the console 5 is a memory 5f to which various
conditions applicable to the X-ray scanning, such as the rotation
speed of the gantry (described subsequently), are stored.
[0025] A display 6 is connected to the console 5 and displays the
results of processing from the processor 5c.
(Explanation Regarding the Dual Energy Method)
[0026] Next, using FIG. 3, the dual energy method, which is an
X-ray scanning method used in the first embodiment and the second
embodiment, is explained.
[0027] Note that in the present embodiment, "half reconstruction"
refers to a method in which, when the gantry 3 (rotation base)
rotates one turn, data for a half turn of the gantry 3 and data for
a fan angle (approximately 2/3 turn) of the X-ray detector 3b are
acquired, and in which reconstruction of the X-ray image is
performed based on the data. "Full reconstruction" refers to a
method in which reconstruction of the X-ray image is performed
based on the data acquired when the gantry 3 rotates one turn. The
"Slow kV switching method" refers to a method in which, as the
gantry 3 rotates one turn, the tube voltage and tube current for
the X-ray scanning are switched. For example, with half
reconstruction, subject's data is acquired in approximately 2/3
turn, and with the remaining 1/3 turn, the X-ray emitting condition
is switched. The "X-ray emitting condition" refers to the current
value (mA) and voltage value (kV) necessary to emit a predefined
X-ray. "Scan" refers to a step in which the X-ray is emitted with
respect to the subject under the first X-ray emitting condition, up
to a step in which the X-ray can be emitted with respect to the
subject under the second X-ray emitting condition. That is, not
only does scanning involve irradiation of the X-ray, but it also
involves a switching step of the current value and voltage value
from the first X-ray emitting condition to the second X-ray
emitting condition, and a step for performing trajectory
specification (described subsequently). "Scan condition" refers to
the X-ray emitting condition, as well as the exposure range within
which X-ray scanning is performed, the moving speed of the bed 4
(the table-top 4a), reconstruction condition (half reconstruction
or full reconstruction), effective field of view, slice thickness,
etc. These values are arbitrarily set by testers. The "trajectory
specification" is a method for specifying, when scanning under the
first and second X-ray emitting conditions, which are different
from each other, a starting point in order to start scanning with
the first X-ray emitting condition and a scan with the second X-ray
emitting condition from the same angle (angle with respect to a
predefined reference direction). By differential processing the
data based on the respective X-ray emitting conditions obtained as
photography is started at the same angle, the X-ray image can be
reconstructed such that effects of artifact are eliminated. The
"trajectory specification angle S [rad]" refers to the angle at
which irradiation is started with the first X-ray emitting
condition and the second X-ray emitting condition (angle with
respect to a predefined reference direction). This angle can be
determined arbitrarily. The "switching start angle A [rad]" refers
to the angle at which switching from the first X-ray emitting
condition (or from the second X-ray emitting condition) to the
second X-ray emitting condition (or to the first X-ray emitting
condition) is started (angle with respect to a predefined reference
direction). This angle is defined by determining the trajectory
specification angle S and the reconstruction condition (full
reconstruction or half reconstruction). The "switching completion
angle B [rad]" refers to the angle at which switching of the X-ray
emitting condition that is started at the switching start angle
completes (angle with respect to a predefined reference direction).
This angle is decided by the X-ray emitting condition. The "first
tube voltage X.sub.k v 1 [kV]" and "first tube current X.sub.m A 1
[mA]" are the tube voltage and tube current constituting the first
X-ray emitting condition. The "second tube voltage X.sub.k v 2
[kV]" and "second tube current X.sub.m A 2 [mA]" are the tube
voltage and tube current constituting the second X-ray emitting
condition. "Interval times Tc [s]" is the time required for
switching from the first X-ray emitting condition to the second
X-ray emitting condition. During this time, irradiation of the
X-ray is stopped. This value is determined from a table, etc.,
based on the combination of the first and second X-ray emitting
conditions. The "rotation speed of the gantry R [s/r]" is the time
taken for the gantry 3 (rotation base) to rotate one turn. The
"full reconstruction view number Nf (R)" is the amount of X-ray
image data that may be obtained when the gantry 3 rotates one turn.
This is the value determined from a table, etc., based on the
rotation speed of the gantry. The "reconstruction view number Nh
(R)" is the amount of X-ray image data that is defined by the scan
condition and the rotation speed of the gantry. For example, for
cases of half reconstruction, the value is obtained from Nh
(R).apprxeq.Nf (R).times.2/3. "Frequency of intermittent emission Y
[r]" shows how many times the gantry 3 rotates in order to perform
one scan. The "number of X-ray emissions" is the number of times
that X-ray emission (the number of scans) is necessary in order to
acquire desired the X-ray image data. For example, if it is set to
"20 scans with the dual energy method," it requires X-ray
irradiation for 20 times (10 scans with the first X-ray emitting
condition and 10 scans with the second X-ray emitting condition).
The "priority condition" refers to, for the display of the results
of X-ray imaging, a determination condition for cases in which
priority is placed on a certain display mode. For example, when a
tester would like to prioritize contrast, "contrast" is selected as
the priority condition. Moreover, when the tester would like to
prioritize time resolution, "time resolution" is selected as the
priority condition.
[0028] FIG. 3 shows a measurement state for a trajectory
specification dual energy scan for half reconstruction.
[0029] First, from the previously defined trajectory specification
angle S, a first scan 110 is started based on the first X-ray
emitting condition. When the first scan 110 is started, the gantry
3 starts the rotation, and at the same time, the X-ray is emitted
from the X-ray emitting part 3a to the subject 2 based on the first
X-ray emitting condition.
[0030] Since in the present embodiment, the half reconstruction
condition is applied, the first scan 110 is performed up to the
position of the switching start angle A. That is, the first scan
110 is performed by turning approximately 2/3 clockwise (right-hand
turn) from the trajectory specification angle S to the switching
start angle A.
[0031] Subsequently, the first X-ray emitting condition is switched
to the second X-ray emitting condition. Since it takes a predefined
time (the interval times Tc) for this action, during this time, the
gantry 3 rotates around the subject 2, in the state in which the
X-ray is not emitted. In FIG. 3, the rotation according to this
switching action is shown as an X-ray switch rotation 111.
[0032] After switching from the first X-ray emitting condition to
the second X-ray emitting condition completed at the switching
completion angle B, rotation of the gantry 3 is required in order
to match the position at which irradiation is started with the
second X-ray emitting condition to the trajectory specification
angle S. In FIG. 3, the rotation according to this trajectory
matching is shown as the trajectory matching rotation 112.
[0033] When the X-ray emitting part 3a inside the gantry 3 reaches
the trajectory specification angle S resulting from the trajectory
matching rotation 112, irradiation of the X-ray is started with the
second X-ray emitting condition. In FIG. 3, the X-ray scanning
under the second X-ray emitting condition is shown as the second
scan 113.
[0034] After X-ray scanning is performed for approximately 2/3 turn
with the second scan, in order to perform a scan with the first
X-ray emitting condition again, the X-ray emitting condition is
switched and trajectory matching is performed. Accordingly, based
on the X-ray image data obtained by scanning the predefined
exposure range, the X-ray image is reconstructed and is displayed
on the display 6.
[0035] In this way, according to the trajectory specification dual
energy scan for half reconstruction, by performing differential
processing of the data based on the first X-ray emitting condition
and the data based on the second X-ray emitting condition, obtained
by starting at the same angle, the X-ray image can be reconstructed
such that artifact effects are eliminated.
[0036] Note that for cases of full configuration, the first scan
110 and the second scan 113 change to one rotation and are changed
after going through the X-ray switch rotation 111 and the
trajectory matching rotation 112.
[0037] Moreover, when performing half reconstruction using the Slow
kV switching method, in the rotation from the switching start angle
A to the trajectory specification angle S, the X-ray emitting
condition is switched. In this case, rotation from the switching
start angle A to the trajectory specification angle S falls under
the X-ray switch rotation 111 and the trajectory matching rotation
112.
First Embodiment
[0038] Next, using FIG. 4 and FIG. 5, the first embodiment is
explained.
[0039] The present embodiment describes the dual energy method scan
for full reconstruction.
[0040] As shown in FIG. 4, the processor 5c according to the
present invention has a determining part 10, an acquiring part 11,
a first calculating part 12, and a second calculating part 13. Note
that the processor 5c performs processing to reconstruct the X-ray
image for displaying on the display 6, based on the X-ray detection
results from the X-ray detector 3b; however, the processing is
generally known; hence, a detailed explanation is omitted.
[0041] The determining part 10 determines the first X-ray emitting
condition and the second X-ray emitting condition for performing
X-ray scanning with the dual energy method, resulting from the
input related to the X-ray emitting condition from the input part
5a. This input is performed as the tester arbitrarily selects from
the plurality of X-ray emitting conditions displayed on the display
6, and as input with the input part 5a. Note that as the tester
inputs arbitrary numerical values (current value and/or voltage
value) with the input part 5a, based on the input, as the
determining part 10 reads out the X-ray emitting condition
corresponding to the input from the plurality of X-ray emitting
conditions previously stored in the memory 5f, it is also possible
to determine the X-ray emitting condition.
[0042] The acquiring part 11 acquires interval times, based on the
first X-ray emitting condition and the second X-ray emitting
condition determined at the determining part 10, for switching the
first X-ray scanning, resulting from the first X-ray emitting
condition, and the second X-ray scanning, resulting from the second
X-ray emitting condition. Interval times is acquired based on a
table, which is stored in the memory 5f, which describes the
relationship between the interval times and X-ray emitting
conditions (the first X-ray emitting condition and second X-ray
emitting condition). That is, when the acquiring part 11 receives
information regarding the X-ray emitting condition from the
determining part 10, it reads out the table in the memory 5f,
specifies the interval times corresponding to this X-ray emitting
condition, and acquires this interval times value.
[0043] The first calculating part 12 calculates the frequency of
intermittent emission of X-rays for the rotation speed of the
gantry based on the rotation speed of the gantry and the interval
times of the gantry 3. The plurality of rotation speeds of the
gantry 3 is stored, for example, in the memory 5f. Moreover,
resulting from the input by the tester, etc., any one of the
rotation speeds of the gantry is selected. For calculation of the
frequency of intermittent emission, Formula (6) or Formula (7),
which are described subsequently, are used. That is, the first
calculating part 12 performs arithmetic processing of the value of
the interval times acquired from the acquiring part 11 and the
rotation speed of the gantry selected by the tester based on
Formula (6) or Formula (7), thereby calculates the frequency of
intermittent emission.
[0044] The second calculating part 13 calculates the exposure time
for sequentially performing the first X-ray scanning and second
X-ray scanning, based on the rotation speed of the gantry 3, the
frequency of intermittent emission calculated at the first
calculating part 12, and the number of X-ray emissions during the
X-ray scanning with the X-ray CT apparatus. Note that the number of
X-ray emissions is determined at the scan condition determining
part 5d, based on the exposure range input by the input part 5a,
the rotation speed, the slice thickness, and a scan condition such
as the helical pitch for cases of helical scanning.
[0045] Next, using FIG. 5, the X-ray scanning action of the dual
energy method, using the X-ray CT apparatus 1, is explained. Note
that step numbers in FIG. 5 are shown as "S numbers."
[0046] First, a tester (physician, etc.) operates the input part
5a, and inputs the scan condition. The scan condition determining
part 5d determines the scan condition based on the input (S10). For
example, for cases in which the condition of the exposure range and
the slice thickness are input, when it is possible to perform X-ray
scanning with the condition (within the exposure range in which the
photography can be performed with the X-ray CT apparatus 1, etc.),
the scan condition determining part 5d determines the scan
condition.
[0047] Moreover, the scan condition determining part 5d transmits
the signals to the controller 5b so as to perform X-ray scanning
under the condition. The controller 5b executes X-ray scanning
according to the condition.
[0048] Next, based on the input of the input part 5a performed by
the tester (physician, etc.), the determining part 10 determines
the first X-ray emitting condition and the second X-ray emitting
condition (S11).
[0049] The first X-ray emitting condition is constituted from the
"first tube voltage X.sub.k v 1 [kV]" and "first tube current
X.sub.m A 1 [mA]." The second X-ray emitting condition is
constituted from the "second tube voltage X.sub.k v 2 [kV]" and
"second tube current X.sub.m A 2 [mA]." These values can be
arbitrarily set by the tester in the operating range of the X-ray
emitting part 3a (within the range of the maximum current (voltage)
and the minimum current (voltage) for X-ray emitting part 3a).
Moreover, the memory 5f may be stored, in advance, a plurality of
values in a selectable manner.
[0050] Next, the acquiring part 11 acquires the interval times Tc,
based on the first X-ray emitting condition and the second X-ray
emitting condition, which are determined at S11. The interval times
Tc is uniquely determined, with respect to the first X-ray emitting
condition and the second X-ray emitting condition. That is, the
interval times Tc, when the first X-ray emitting condition and the
second X-ray emitting condition are determined, is uniquely
acquired based on the table stored in the memory 5f.
[0051] Next, the first calculating part 12 calculates the frequency
of intermittent emission with respect to the rotation speed of the
gantry R from the interval times Tc acquired at S12 and the
rotation speed of the gantry R that is determined based on the
selection by the tester (S13).
[0052] Here, the formula showing a relationship between the
interval times Tc, the rotation speed of the gantry R, and the
frequency of intermittent emission Y is explained in detail, using
FIG. 3.
[0053] In FIG. 3, an angle SA required to move from the trajectory
specification angle S to the switching start angle A is shown in
the following Formula (1), using the full reconstruction view
number Nf and the reconstruction view number Nh.
[ Formula 1 ] SA = 2 .pi. .times. Nh Nf ( 1 ) ##EQU00001##
[0054] Moreover, in FIG. 3, the angle AB required to move from the
switching start angle A to the switching completion angle B is
shown in the following Formula (2), using angular speed
.omega.(.omega.=2.pi./R) and the interval times Tc.
[Formula 2]
AB=.omega..times.Tc (2)
[0055] Moreover, in FIG. 3, the angle BS required to move from the
switching completion angle B to the trajectory specification angle
S is shown in the following Formula (3), using the rotation speed
of the gantry R, the full reconstruction view number Nf, the
reconstruction view number Nh, the angular speed .omega., and the
interval times Tc.
[ Formula 3 ] BS = 2 .pi. - mod ( 2 .pi. .times. Nh Nf + .omega.
.times. Tc , 2 .pi. ) = 2 .pi. - mod ( 2 .pi. .times. Nh Nf + 2
.pi. R .times. Tc , 2 .pi. ) = 2 .pi. - 2 .pi. .times. mod ( Nh Nf
+ Tc R , 1 ) ( 3 ) ##EQU00002##
[0056] Note that Y=mod(X,A) means that "Y is the remainder after X
is divided by A." What is meant by Y=mod(X,1) is that "Y is a value
less than or equal to the decimal point of X."
[0057] Next, X-ray scanning is performed with the first X-ray
emitting condition (or the second X-ray emitting condition), and
the time taken to switch to the second X-ray emitting condition (or
the first X-ray emitting condition), that is, the moving time tx in
which the angle changes S.fwdarw.A.fwdarw.B.fwdarw.S, is shown in
the following Formula (4), using the rotation speed of the gantry
R, the full reconstruction view number Nf, the reconstruction view
number Nh, the angular speed .omega., and the interval times
Tc.
[ Formula 4 ] tx = R .times. Nh Nf + Tc + BS .omega. = R .times. Nh
Nf + Tc + BS .times. R 2 .pi. = R .times. Nh Nf + Tc + R - R
.times. mod ( Nh Nf + Tc R , 1 ) ( 4 ) ##EQU00003##
[0058] Here, the frequency of intermittent emission Y is shown in
the following Formula (5), using the moving time tx during the
angle S.fwdarw.A.fwdarw.B.fwdarw.S and the rotation speed of the
gantry R.
[ Formula 5 ] Y = tx R ( 5 ) ##EQU00004##
[0059] From Formula (4) and Formula (5), the frequency of
intermittent emission Y is shown in the following Formula (6).
[ Formula 6 ] Y = Nh Nf + Tc R + 1 - mod ( Nh Nf + Tc R , 1 ) ( 6 )
##EQU00005##
[0060] Here, for cases of full reconstruction, it becomes Nh/Nf=1,
and the frequency of intermittent emission Y is shown in the
following Formula (7).
[ Formula 7 ] Y = 2 + Tc R - mod ( Tc R , 1 ) ( 7 )
##EQU00006##
[0061] That is, at S13, the first calculating part 12 calculates
the frequency of intermittent emission based on Formula (6) or
Formula (7) above.
[0062] For example, as is clear from formula (7), if Tc<R, as
the gantry 3 rotates 2 turns, the first scan and the second scan
are performed alternately. In contrast, if Tc>R, as it rotates 3
turns, the first scan and the second scan are performed
alternately.
[0063] Next, the scan condition determining part 5d calculates the
number of X-ray emissions necessary for the X-ray scanning based on
the scan condition selected by the tester (S14). Note that with
regard to the number of X-ray emissions, it may be determined when
the scan condition is determined at S10.
[0064] Based on the rotation speed of the gantry R determined based
on the selection by the tester, the frequency of intermittent
emission calculated at S13, and the number of X-ray emissions
calculated at S14, the second calculating part 13 calculates the
total time required for the X-ray scanning (exposure time [s])
(S15). The calculated exposure time, for example, after being
combined with other test conditions by a display controller, not
shown in the figures, is displayed on the display 6. Therefore, the
tester is able to figure out the first X-ray emitting condition and
the second X-ray emitting condition, which are determined based on
the tester's own selection, as well as the exposure time resulting
from the rotation speed of the gantry R.
[0065] When the tester determines that it is appropriate to conduct
tests with the exposure time calculated at S15, the tester inputs
with the input part 5a, providing a command to start operating the
X-ray CT apparatus 1. Accordingly, as the controller 5b, controls
the action of the X-ray CT apparatus 1 based on the condition
determined from S10 to S15, the X-ray scanning of the dual energy
method is started (S16).
[0066] Note that, as above, generally, the plurality of rotation
speeds of the gantry are stored in the X-ray CT apparatus.
Therefore, it is also possible to calculate the frequency of
intermittent emission for all of the rotation speeds of the gantry
stored in the X-ray CT apparatus. In this case, it is possible to
display a table providing each condition, such as Table 1 shown
below, on the display 6 and have the tester select any
condition.
TABLE-US-00001 TABLE 1 Exposure Exposure condition R[s/r] Y[r] time
[s] 1 0.3 3 18 2 0.4 3 24 3 0.5 2 20
[0067] In Table 1, for any of these conditions, the X-ray emitting
condition is the same. Moreover, the number of X-ray emissions is
set to 20 times. Note that each numerical value in Table 1 is for
illustrative purposes only, so as to make it easy to understand the
present embodiment; hence it is not limited to these.
[0068] Because Table 1 is displayed on the display 6, the tester
can easily recognize that when the X-ray scanning is performed with
the exposure condition "1," X-ray scanning can be performed (time
resolution being high) with the shortest exposure time (total
exposure time).
[0069] On the other hand, for cases in which photography is
performed using the helical scanning method, the larger the value
of the frequency of intermittent emission Y, the smaller the
overlapping section of the X-ray image data taken with each X-ray
emitting condition. That is, for cases in which the helical
scanning method is used, the larger the frequency of intermittent
emission, the smaller the contrast of the X-ray image. Even in
cases of this type, based on Table 1 displayed on the display 6,
the tester is able to determine whether to select the exposure
condition "1" in which time resolution is prioritized or the
exposure condition "3" in which contrast is prioritized.
[0070] Moreover, based on the input command from the input part 5a,
it is also possible to select a time resolution priority or a
contrast priority for the priority condition selecting part 5e. In
this case, by executing the above processing, it can be constituted
so as to display, on the display 6, only the exposure condition
corresponding to the previously selected condition.
[0071] On the other hand, it is also possible to display on the
display 6, so as to recommend the exposure condition matching the
previously selected condition. For example, for cases of "time
resolution priority," it is possible to display such that the frame
for the exposure condition "1" in Table 1 or characters displayed
within this frame are displayed in different display colors.
[0072] Furthermore, depending on the relationship between the
rotation speed of the gantry and the frequency of intermittent
emission, the exposure time may be equal. For example, for cases
when R=0.4 [s/r] and Y=3, and for cases when R=0.6 [s/r] and Y=2,
for both cases, the X-ray is emitted for each 1.2 [s]. Therefore,
if the number of X-ray emissions is set to 20 times, for both
cases, an exposure time of 24 [s] is required. Even in cases of
this type, because a list of the exposure conditions as shown in
Table 1 is displayed, the tester can easily select the exposure
condition (for cases of R=0.6 [s/r] and Y=2) for prioritizing the
contrast. This selection may also be performed automatically, based
on the scan condition, etc., determined in advance.
[0073] Furthermore, the interval times Tc1 for cases of switching
from the first X-ray emitting condition to the second X-ray
emitting condition and the interval times Tc2 for cases of
switching from the second X-ray emitting condition to the first
X-ray emitting condition may differ.
[0074] Even in such cases, it is possible to calculate, from
Formula (7), the frequency of intermittent emission Y1 and Y2, with
respect to each interval times, and calculate the total exposure
time based on the rotation speed of the gantry and the number of
X-ray emissions. Note that in this case, in Table 1, it is also
possible to display both frequencies of intermittent emission Y1
and Y2.
[0075] Note that among the items described in Table 1, for the item
to be displayed on the display 6, either one may be displayed.
Moreover, it is also possible to display the first X-ray emitting
condition and the second X-ray emitting condition.
[0076] Even for cases of half reconstruction, using Formula (6), it
is possible to calculate the exposure time by calculating the
frequency of intermittent emission Y.
[0077] As above, according to the present embodiment, based on
Formula (6) or Formula (7), it is possible to calculate the
frequency of intermittent emission of the X-ray and display the
exposure condition including this value on the display 6.
Therefore, because the tester can arbitrarily select the exposure
condition, desired tests can be conducted effectively.
Second Embodiment
[0078] Next, using FIG. 6 and FIG. 7, the second embodiment is
explained. In the present embodiment, the dual energy method for
full reconstruction is described.
[0079] As shown in FIG. 6, a processor 5c in the present
embodiment, as is the case with the first embodiment, has a
determining part 10, an acquiring part 11, a first calculating part
12, and a second calculating part 13. Note that the action of the
second calculating part 13 is the same as the first embodiment;
hence, an explanation is omitted.
[0080] The determining part 10 in the present embodiment determines
the rotation speed of the gantry 3 and the frequency of
intermittent emission, resulting from the input command from the
input part 5a. The input command is arbitrarily selected by a
tester, from the plurality of rotation speeds of the gantry or the
frequencies of intermittent emission displayed on the display 6,
and is carried out as input at the input part 5a. Or, for cases in
which a plurality of gantry rotations and the frequencies of
intermittent emission with respect thereof are associated and
stored in the memory 5f and a rotation speed of the gantry is
determined, the frequency of intermittent emission may be uniquely
determined.
[0081] The first calculating part 12 in the present embodiment,
based on the rotation speed of the gantry and the frequency of
intermittent emission determined at the determining part 10,
calculates the interval times for switching the first X-ray
scanning with the first X-ray emitting condition, and the second
X-ray scanning with the second X-ray emitting condition. For
calculating interval times, Formula (6) or Formula (7) described in
the first embodiment is used. That is, the first calculating part
12 performs arithmetic processing with respect to the rotation
speed of the gantry and the frequency of intermittent emission,
which are determined by the determining part 10, based on Formula
(6) or Formula (7), and calculates interval times.
[0082] The acquiring part 11 in the present embodiment acquires the
first X-ray emitting condition and the second X-ray emitting
condition based on the interval times calculated at the first
calculating part 12.
[0083] As described in the explanation for the first embodiment,
the interval times Tc, for cases in which the first X-ray emitting
condition and the second X-ray emitting condition are determined,
is a value that is uniquely acquired based on the table stored in
the memory 5f.
[0084] Therefore, from the interval times calculated at the first
calculating part 12, the acquiring part 11, based on the table
stored in the memory 5f, can uniquely acquire the first X-ray
emitting condition and the second X-ray emitting condition. That
is, when the acquiring part 11 receives information regarding the
interval times Tc from the first calculating part 12, it reads out
a table in the memory 5f, specifies the first X-ray emitting
condition and the second X-ray emitting condition corresponding to
the interval times, and acquires values for the first X-ray
emitting condition and the second X-ray emitting condition.
[0085] Next, using FIG. 7, the X-ray scanning action for the dual
energy method is explained, using the X-ray CT apparatus 1. Note
that the step number in FIG. 7 is shown in "S numbers."
[0086] First, as a tester (physician, etc.) operates the input part
5a and inputs the scan condition, the scan condition determining
part 5d determines the scan condition (S20). For example, for cases
in which input is performed with regard to the condition of the
exposure range and the slice thickness, the signals are transmitted
to the controller 5b so as to perform X-ray scanning under the
condition. The controller 5b executes X-ray scanning under the
condition. Note that the range of the scan conditions that can be
determined for each X-ray CT apparatus varies.
[0087] Next, for cases in which a rotation speed of the gantry is
selected at the input part 5a by a tester, etc., the determining
part 10 determines the rotation speed of the gantry R, which is
selected from the plurality of rotation speeds of the gantry stored
in the memory 5f (S21).
[0088] Next, for cases in which a frequency of intermittent
emission is selected at the input part 5a by a tester, etc., the
determining part 10 determines the frequency of intermittent
emission Y, which is selected from the plurality of frequencies of
intermittent emission stored in the memory 5f (S22). Note that S21
and S22 may be performed simultaneously or the sequence may be
reversed.
[0089] Next, the first calculating part 12 calculates the interval
times Tc based on the rotation speed of the gantry R and the
frequency of intermittent emission Y (S23). The relationship
between the rotation speed of the gantry, the frequency of
intermittent emission, and the interval times is shown in the above
Formula (7). That is, as is the case with the first embodiment,
utilizing the relationship between the rotation speed of the
gantry, the frequency of intermittent emission, and the interval
times, it is possible to calculate a desired value (in the present
embodiment, interval times).
[0090] Next, the acquiring part 11, based on the interval times Tc,
acquires the first X-ray emitting condition and the second X-ray
emitting condition (S24). As above, based on the interval times
calculated at the first calculating part 12, the acquiring part 11
uniquely acquires the first X-ray emitting condition and the second
X-ray emitting condition, using the table stored in the memory
5f.
[0091] Next, the scan condition determining part 5d calculates the
number of X-ray emissions required for the X-ray scanning based on
the scan condition selected by a tester, etc. (S25). Note that the
number of X-ray emissions may be determined in advance when the
scan condition is determined at S10.
[0092] Based on the rotation speed of the gantry R determined at
S21, the frequency of intermittent emission Y determined at S22,
and the number of X-ray emissions determined at S25, the second
calculating part 13 calculates the total time (the exposure time
[s]) for the X-ray scanning (S26). For the X-ray emitting condition
calculated at S24 and the exposure time determined at S26, for
example, after they are combined with other test conditions by the
display controller, not shown in the figures, they are displayed on
the display 6. Therefore, it is possible for the tester to
understand the X-ray emitting condition and the exposure time,
based on the rotation speed of the gantry and the frequency of
intermittent emission, which are determined based on the tester's
own selection.
[0093] When the tester determines that it is appropriate to conduct
a test with the exposure time calculated at S26, the tester
performs input action with the input part 5a, providing a command
to start the operation of the X-ray CT apparatus 1. Accordingly, as
the controller 5b controls the action of the X-ray CT apparatus 1,
based on the condition determined from S20 to S26, the dual energy
method X-ray scanning is started (S27).
[0094] In the above explanation, one frequency of intermittent
emission Y is selected and the exposure time, etc., are calculated;
however, for example, with respect to any one of the rotation
speeds of the gantry, it is possible to determine values of the
plurality of frequencies of intermittent emission and calculate the
exposure time, etc., with respect to each value.
[0095] Moreover, displayed on the display 6 is at least one of the
rotation speed of the gantry, the frequency of intermittent
emission, the first X-ray emitting condition, the second X-ray
emitting condition, and the exposure time.
[0096] Moreover, even for cases of half reconstruction, processing
in the present embodiment can be executed using Formula (6).
[0097] Even for cases in which the rotation speed of the gantry or
the frequency of intermittent emission are determined in advance,
as is the case with the present embodiment, based on Formula (6) or
Formula (7), by calculating the interval times at the first
calculating part 12, it is possible to determine the X-ray emitting
condition. Therefore, it is possible to display the information on
the display 6, making it easy for the tester to determine the
exposure condition.
(Common Items for the First and Second Embodiments)
[0098] The abovementioned exposure condition processing method of
the X-ray CT apparatus and the X-ray CT apparatus may be the
helical scanning method or the dynamic volume scanning method.
[0099] Moreover, it is also possible to program the above
processing details and cause a computer to execute them.
[0100] As above, according to the present embodiment, among the
processing results of the processor 5c, the exposure conditions
necessary for the X-ray scanning can be displayed on the display
6.
[0101] Therefore, since a tester is able to arbitrarily select the
exposure condition, desired tests can be effectively conducted.
[0102] While certain embodiments have been described, these
embodiments have been presented by way of example only, and are not
intended to limit the scope of the inventions. Indeed, the novel
systems described herein may be embodied in a variety of their
forms; furthermore, various omissions, substitutions and changes in
the form of the systems described herein may be made without
departing from the spirit of the inventions. The accompanying
claims and their equivalents are intended to cover such forms or
modifications as would fall within the scope and spirit of the
inventions.
* * * * *